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If the Pokémon with this Ability is confused and is holding a Persim or Lum Berry, the Berry will be eaten before Own Tempo cures the Pokémon of confusion.
Note that the first post on the Smogon SV research thread still says that Protosynthesis and Quark Drive are immune to Gastro Acid, so it's probably worth posting your update there too. (I would, but in this case I didn't do the research myself.)
Research Thread 'Scarlet & Violet Battle Mechanics Research'
Note: Version numbers are used to show that a new version of the games was released between tests within a given list, and that mechanics following the heading were tested using that version, not to imply that those mechanics necessarily changed from a previous version unless otherwise indicated in this or the linked post.
New Mechanics in Scarlet and Violet
Terastal